1. Filed of the Invention
The present invention relates to an electro-photographic system image forming apparatus employed in the copying machine, the printer, etc. and, more particularly, an image forming apparatus using a contact transfer system.
2. Description of the Related Art
In the related art, an electro-photographic system image forming apparatus employed in a copying machine, a printer, etc. employs a non-contact type transcriber utilizing a corona discharge as a transcriber that transfers a toner image formed on an photoreceptor onto a recording medium. However, since the ozone is generated during the corona discharge in this system, the contact type transcriber that generates the less ozone is developed.
The contact type transcriber supplies transfer current to the recording medium, which is nipped between a transfer member and the photoreceptor, while applying the transfer bias to the transfer member to adsorb the toner image formed on the photoreceptor onto the recording medium side.
However, mainly a transfer roller is employed as the contact type transfer member. There is a problem that, since this transfer roller has a structure that comes into direct contact with the photoreceptor, the toner on the photoreceptor adheres to the transfer roller and thus a surface of the transfer roller is contaminated.
In order to overcome this problem, a method of cleaning mechanically the surface of the transfer roller by the blade has been proposed.
However, if a foamed sponge, or the like is employed on the transfer roller in view of the cost, the material, etc., the toner enters into pores of the roller surface and therefore sufficient cleaning is not achieved.
Consequently, cleaning technology by utilizing the static electricity is disclosed in JP-A-Hei. 3-69978, for example.
The disclosed technology is that bias between a charger and a developer is stopped after the last paper in an image forming process passes through, then a normally charged toner is reversely transferred onto a photoreceptor side by applying bias voltage having the same polarity as the toner to a transfer roller, and then a reversed toner is also reversely transferred onto the photoreceptor side by applying the bias voltage having the reverse polarity.
However, when the bias voltage having the reversed polarity is applied, the normally charged toner is transferred again onto the transfer roller and therefore it is impossible to execute the sufficient cleaning. In JP-A-Hei. 8-248788, such a technology is disclosed that the bias having the same polarity as the toner is applied to the transfer roller after the last paper in the image forming process passes through and then the bias having the opposite polarity to the toner is applied to the transfer roller before the first paper in the image forming process passes through.
However, if the bias having the opposite polarity to the toner is applied before the first paper passes through, the history is generated in the photoreceptor by the transfer bias. Therefore, the charging of the photoreceptor must be executed twice or more to erase this history, and thus it takes too much processing time.
Therefore, in JP-A-Hei. 11-143145, such a technology is disclosed that the cleaning is carried out after the transfer is completed and that the potential difference is reduced rather than that in the development, e.g., only the DC component is applied as the developing bias when the development is not executed.
According to these technologies, since the cleaning of the transfer roller is carried out after the last paper in the image forming process passes through, the time required from the start command in the last image forming cycle to the output of the image which is formed on the first recording medium (so-called FPOT: first printout time) can be reduced.
However, after the last image forming cycle is finished, in some cases the processes of detecting the current by applying the bias voltage to the transfer roller to grasp the resistance characteristic of the transfer roller with the environmental change and then correcting the bias voltage that is to be applied to the transfer roller in the subsequent image forming process, in addition to the above cleaning process of the transfer roller, are carried out in order to reduce the FPOT and assure the good transferring characteristic.
Since these processes, once started, are continued until they are completely ended, the process cannot immediately shift to the image forming process even if the image formation restart command is issued. As a result, the FPOT can be reduced, but sometimes the throughput is extremely degraded.
In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus capable of reducing the FPOT and also shortening the throughput by restarting quickly the image forming process even after the image forming process is completed once.
In order to achieve the above object, an image forming apparatus according to the invention for executing an image forming cycle in which a toner image is formed in response to an image formation start command and an image formed of a fixed toner image is formed on a recording medium by transferring and fixing the toner image onto the recording medium, the image forming apparatus for executing a predetermined post-process cycle when a subsequent image formation start command is not issued within a predetermined time after the last image forming cycle is ended, the image forming apparatus comprising a sequence controlling section adapted to stop the post-process cycle when receiving the sequent image formation start command during executing the post-process cycle, to shift to execute a subsequent image forming cycle.
Here, it is preferable that the post-process cycle is a plurality of post-processes that are sequentially continued and the sequence controlling section shift-to execute the image forming cycle at a timing when the post-process, that is being executed, out of the plurality of post-processes is ended, when receiving the sequent image formation start command during executing the post-process cycle.
Here, it is preferable that the image forming apparatus further comprises a transferring member for transferring the toner image onto the recording medium and the post-process cycle includes a process of cleaning the transferring member.
Here, it is preferable that the image forming apparatus further comprises a transferring member for transferring the toner image onto the recording medium, a bias applying section adapted to apply a transfer bias voltage to the transferring member, and a current detecting section adapted to detect a transfer current that flows by applying the transfer bias voltage to the transferring member and that the post-process cycle includes a process of detecting a relationship between the transfer bias voltage and the transfer current.
Here, it is preferable that the image forming cycle includes a pre-process that is executed when the subsequent image formation start command is received after the post-process cycle is completed, and an image forming process that is executed subsequently to the pre-process and is executed when the subsequent image formation start command is issued before the image forming cycle is completed or within a predetermined time after the image forming cycle is completed and that when the subsequent image formation start command is issued during the post-process cycle is being carried out and then the post-process cycle is stopped to execute the image forming process, the sequence controlling section executes the image forming process by omitting the pre-process.